This invention relates generally to the manufacture of electronic devices and more particularly to the testing chips used to make smart cards during their manufacture. xe2x80x9cSmart cardsxe2x80x9d refers to a new type of device that is highly portable but can store information in digital form. Smart cards can be made with dimensions of a few centimeters by a few centimeters with a thickness of less than a millimeter. They can be made, for example in the size of a conventional credit card. When held near a device called a xe2x80x9creader,xe2x80x9d the smart card can exchange information with a computerized system.
There are many applications for smart cards. One example of a smart card, is identification cards used in connection with building security systems. An identification card can be issued to each person using the building and will store a security code unique to that individual. Readers can be placed near locked doors in the building. When the identification card is held near the reader, the reader can access the security code on the smart card. The security system can then know which individual wishes to pass through the locked door and only unlock the door if that person is authorized.
In some countries, smart cards are being used to replace standard credit or debit cards. In addition to storing identifying information about authorized users of the card, the card could store data about transactions or account balances. Others have attached smart cards to livestock in herds such that the activities of each individual animal can be tracked. Others propose that identification cards, or xe2x80x9ctagsxe2x80x9d, be attached to articles for sale in stores for price labeling and inventory control. Herein, the term xe2x80x9csmart cardxe2x80x9d will be used to generally describe devices such as credit cards with embedded chips, identification cards and tags as described above. Though it should be appreciated that smart cards come in many forms.
There are many applications for smart card technology, though the wide spread use depends on such devices being relatively low cost and also being reliable. Thus, it is highly desirable for the manufacturing operation for smart cards, including testing, to be low cost and lead to reliable products. Low cost is particularly important for smart cards used for identification cards or tags.
In some smart cards, the chips inside the smart cards communicate with the reader through direct connections. However, some smart cards communicate with a reader through an RFID interface without direct contact between the card and the reader. The integrated circuit chip inside the smart card both communicates and receives power to operate through the RFID interface. The reader generates an RF carrier signal. A conducting loop is embedded in the smart card and is attached to terminals of the integrated circuit chip. The RF signal couples through this loop to the integrated circuit chip. Circuitry inside the integrated circuit chip can rectify the received carrier signal and extract the power needed to operate the entire chip.
The RF carrier signal is also used to convey information between the reader and the integrated circuit chip. To send information from the reader to the smart card, the reader modulates the carrier signal. The chip can demodulate the carrier and extract the information. To send information back, the integrated circuit chip in the smart card changes the impedance at its terminals connected to the conducting loop. In much the same way that changing the load on one side of a transformer changes the signal on the other side of a transformer, a change in the impedance at the terminals of the chip on the smart card causes a measurable effect to a signal in the reader. By modulating the impedance at its terminals, the smart card can modulate a signal that can be detected on the reader and thus send information to the reader.
Generally, integrated circuit chips are tested during their manufacture with automated test equipment. This equipment is designed to test many chips rapidly, because high throughput in a manufacturing operation usually leads to lower cost. The Integra J750 sold by Teradyne, Inc. is an example of a test system well suited for low cost test of semiconductor devices and can test many devices in parallel.
However, such testers are not directly applicable to testing smart card chips. One problem is that it is difficult to get access to the chips for testing, particularly for chips intended for use with an RFID interface. It would be desirable to test the chips before they are embedded in cards, but, until the chips are embedded into cards, they are not connected to the conductive loop that provides power and communications with the chip. One way that this problem has been solved is through the use of special purpose test devices.
Another difficulty is that existing automatic test equipment designed for testing low cost digital signals is not equipped to demodulate RF signals. While some testers, such as the Catalyst sold by Teradyne, Inc. do contain instruments that could demodulate an RF signal, such testers are not well suited for fast testing of many small and low cost devices. One way that this problem has been solved is through modification of the chips to include a test port so that the load imposed by the chip at its I/O terminals can be measured. However, the increase in size of the chip to accommodate the test port is undesirable because it increases the overall cost of the chip. In addition, a traditional test system measures a load as a dc measurement using a parametric measurement unit (PMU). Use of the PMU is undesirable because it leads to slow testing. Further, when testing is done through test ports, the RFID interface is not included in the test and a chip with a faulty RFID might be passed as good.
Another difficulty is that it would be desirable to test many devices at the same time to reduce the total cost of manufacturing smart cards, but current automatic test equipment is not well suited for this purpose because the time at which each chip responds to commands might vary.
A further difficulty is that some smart card chips vary the load at their I/O terminals by changing the resistance between the terminals. Other smart card chips vary the load by changing the capacitance. The modulation on the carrier signal will be in different form, depending on the type of load imposed. If a general purpose tester were to be used to test smart card chips, it would be highly desirable if it would work on all types of smart card chips, regardless of whether the chip modulated the carrier with a resistive or a capacitive load.
With the foregoing background in mind, it is an object of the invention to enable low cost test of integrated circuit chips intended for use in smart cards.
The foregoing and other objects are achieved in an automatic test system having circuitry that can interface to a chip through an RF interface.
One inventive feature is that the automatic test system has circuitry to modulate a RF carrier signal with data that is synchronized to circuitry in the tester that can generate and measure digital signals.
Another inventive feature is that the automatic test system has circuitry to demodulate a RF carrier signal.
Another inventive feature is that the automatic test system can synchronize responses of multiple chips so that the results of multiple chips can be simply evaluated in parallel.